The present invention relates to a method for recovering an organic solvent from a waste stream containing the organic solvent, acid and other contaminants. The method of the present invention is especially useful for treating waste streams that contain hydrofluoric acid and the organic solvent along with contaminants from etching in fabricating integrated circuit products. The organic solvent of especial interest according to the present invention is propylene carbonate.
In the fabrication of microelectronic components, a number of the steps involved, for instance, in preparing integrated circuit chips and the packaging for the chips (articles to which the chips are attached and protected) are etching processes. Accordingly, over the years, a number of vastly different types of etching processes to remove material, sometimes in selective areas, have been developed and are utilized in varying degrees. Moreover, the steps of etching different layers which constitute, for instance, the finished integrated circuit chip, are among the most critical and crucial steps.
One method widely employed for etching is to overlay the surface to be etched with a suitable mask and then immerse the surface and mask in a chemical solution which attacks the surface to be etched, while leaving the mask intact and while only etching other materials of the article to at most, a minimum extent.
Recently, selective etch processes employing etching compositions comprising hydrofluoric acid (HF) and an organic solvent, preferably propylene carbonate, have been developed and suggested for etching various materials. Use of these compositions has provided improved properties such as a wider process window as well as enhanced selective performance.
However, use of these etching compositions results in waste streams containing the hydrofluoric acid, organic solvent, and a wide variety of etchant contaminants such as silicon dioxide, silicon nitride, ammonium fluoride (NH4F) and the like.
It would therefore be desirable to provide a method for treating the waste stream at least from both economic and environmental viewpoints. Moreover, proper recovery of the solvent would yield for reuse, a superior etchant as regards process control and function.
The present invention relates to a method for treating a waste stream that contains both hydrofluoric acid and an organic solvent to remove the hydrofluoric acid and recover the organic solvent. In particular, the present invention provides a method that is reasonable from an economic viewpoint for recouping and repurifying the organic solvent in the contaminated waste stream. Accordingly, the present invention is beneficial from an ecological viewpoint along with reducing or avoiding waste disposal, reducing waste disposal costs, and reducing raw materials purchase costs.
In particular, the method of the present invention relates to treating a waste stream that comprises hydrofluoric acid, an organic solvent and etchant contaminants by separating the hydrofluoric acid from the waste stream to thereby obtain a first composition containing the hydrofluoric acid and a second stream containing the organic solvent and being at least substantially free, if not entirely free, of the hydrofluoric acid. The separation can be carried out by one or more of the following steps:
a. subjecting the waste stream to ion exchange;
b. extraction of the hydrofluoric acid from the waste stream;
c. subjecting the waste stream to electrophoresis;
d. converting the hydrofluoric acid to a salt insoluble in the waste stream.
Next, the second stream containing the organic solvent is distilled in order to recover the organic solvent free of the etching contaminants.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.